varying float vElevation;

uniform vec3 uLowColor;
uniform vec3 uHighColor;
uniform float uOpacity;

void main() {
    float a = (vElevation) * 10.0;
    vec3 mixColor = mix(uLowColor, uHighColor, a);//和物体局部空间坐标y值有关

    gl_FragColor = vec4(mixColor, uOpacity);
}